In order to cope with high data rate next-generation wireless services, macro cellular cells are usually split into smaller size cells such as picocells and femtocells, helping to increase the spectrum utilization as well as the total system capacity. In such systems, adjacent cells may share the same radio frequency in order to achieve high spectrum efficiency. However, this can give rise to inter-cell interference (ICI).
Inter-cell interference is a particularly serious problem in future small base station scenarios, due to the large number of deployed small cells and their overlapping coverage areas. Without a proper resource allocation method, cell edge users CEUs (i.e. those users who are located close to the edge of a cell's area of geographic coverage) may experience severe interference from neighbouring cells, significantly decreasing the edge user throughput and even resulting in user outage.
Previous approaches for overcoming the ICI problem have focused mainly on the maximization of sum capacity, whereby a cell centre user CCU (i.e. a user who is not located close to the boundary with another cell) having a high throughput is given higher priority when allocating spectrum resources. Nevertheless, user fairness needs to be considered such that reliable services for users at the boundary of the cell (CEU) can be guaranteed.
Fractional frequency reuse (FFR) is another technique to address the ICI problem. In FFR, the numbers of allocated channels (subcarriers or resource blocks) for CEUs and CCUs are independently predetermined for every single adjacent cell. Each cell then assigns a different subset of channels to their cell edge users. In FFR, such a fraction of dedicated channels are reserved for cell edge users in order to achieve a good cell-edge performance. Doing so, however, results in low spectrum efficiency and mat significantly reduce the total cell throughput as these channel resources cannot be reused by cell centre users of the adjacent cells. Soft Frequency Reuse (SFR), on the other hand, uses different subcarrier power levels for CCUs and CEUs, where a low power is used for CCUs and a high power is used for CEUs. As a result, the SFR achieves higher spectrum efficiency than the FFR.
In addition, other techniques such as Proportional Fair (PF) scheduling have been proposed for maximizing the total cell throughput, while allowing all users at least a minimal level of service.
Although techniques such as PF, FFR and SFR consider both user fairness and aggregated user throughput, most of the proposed algorithms cannot guarantee the throughput of cell edge users. It is also desirable that the transmission power of each subcarrier in the respective cells should be allocated optimally for the given set of users, which is not the case when using these techniques.
It follows that there is a need to provide techniques for distributing radio resources fairly between users, whilst helping to ensure the throughput of cell edge users.